1. Field of the Invention
This invention concerns punch presses equipped with rotary turrets for holding punches and dies in which workpieces are moved by a carriage and cross slide located within the throat of the press, such presses often referred to as "rear address" machines.
2. Description of the Prior Art
Punch presses have long been used for forming holes in sheet material. Modern equipment uses a carriage supporting a cross slide having workpiece engaging grippers to automatically move a sheet workpiece so as to bring particular locations on the sheet to a punching station. In turret punch presses, a number of punches and dies are mounted in respective upper and lower turrets which are rotated to bring a selected punch and die combination to the punching station.
The punch press typically has a C-shaped frame, with the punch ram mounted to the front of an upper portion of the frame so that the sheet workpiece can be moved into the opening formed by the C-shaped frame configuration for punching holes in the regions remote from the sheet edge advanced into the opening.
In many presses, referred to as front address machines, the carriage and cross slide are mounted on an extension of the base portion of the frame located to the front of the machine, the carriage moving towards the punching station from its furthest retracted position. This limits the sheet size due to the constraint imposed by the limited distances from the retracted carriages to the punching location and from the punching station to the back of the press frame throat.
As an alternative, some punch presses utilize so called "rear address" configurations, in which the carriage and cross slide, as well as a fixed table are located within the press frame throat. The carriage moves out along a Y-axis from a retracted position adjacent the back of the throat opening towards the punch station. The workpiece is thus free to extend out from the press frame and may be oversized in the Y-axis direction, and is more easily turned for carrying out punching operations on the previously unreachable section.
This rear address punch press configuration often involves a deeper and wider throat opening to accommodate the carriage, cross slide and table.
The ram is powered by a ram drive means such as mechanical slider crank mechanism or a hydraulic drive capable of generating many tons of force. Such force levels requires a heavy frame construction to avoid excessive deflection for the rear address machines.
Heretofore, the upper and lower turrets have been mounted aligned within the press frame. The upper turret is mounted on the upper portion of the frame C-shape. This increases the need for a rigid frame, as the upper turret tends to be misaligned by deflection of the frame.
The large size frame required increases manufacturing and shipping costs.
The mounting of the turrets in the frame opening also restricts the diameter of the turrets, which in turn limits the number of tools which can be stored.
Another disadvantage is that it is more difficult for manufacturers to offer presses having differing turret sizes, since the turrets are integrated into the press, and different press models would have to be produced to offer different turret sizes.
U.S. Pat. No. 3,938,416 issued on Feb. 17, 1976, for "Punching or Nibbling Presses Having a Turret" describes a punch press incorporating a separate frame for a turret assembly. In that arrangement, a workpiece supporting circular fixed table is associated with the separate turret frame, and is transported with movable tables which swing about the fixed table perimeter.
Thus, that press configuration does not have improved capabilities in regard to the punch press of the state of the art, and indeed is more limited in some respects as to its sheet handling ability.
Another problem with the turret equipped punch press is that several dies must often be provided for each punch, since different die clearances are required for various materials. Since equal number of storage locations are in each turret, this limits the number of such configurations, necessitating increased tool changing and, adversely affecting productivity.
Since turrets are driven synchronously, a plurality of duplicate punches are needed, one for each different die clearance, increasing tooling costs and the time to set up tooling.
An object of the present invention is to provide an improved configuration of a punch press equipped with tool storing turrets to lessen or avoid the above-described problems.